In the manufacturing processes for integrated circuits, a lithography process is frequently used for reproducing circuits and structures on a semiconductor substrate. As a first step in a lithography process, a photoresist layer is first coated onto a semiconductor substrate such that an image can be projected and developed on the substrate. The photoresist material is a liquid that is coated in a very thin layer on top of the semiconductor substrate. In a conventional process for applying a photoresist coating material to a semiconductor substrate, a spin coating apparatus is normally used. The spin coating apparatus is a sealed chamber constructed by an upper compartment, a lower compartment and a circular-shaped, rotating platform that has a diameter slightly smaller than the diameter of a semiconductor substrate. The rotating platform is a vacuum chuck since vacuum is applied to the platform for holding the semiconductor substrate securely during a spin coating process. The rotating platform is positioned in the coating machine such that a semiconductor substrate may be placed on top horizontally. During the coating process, the bottom or the uncoated surface of a semiconductor substrate contacts the rotating platform. A suitable vacuum is then applied to the bottom surface of the substrate such that it stays securely on the vacuum chuck even at high rotational speed. The rotating motion of the vacuum chuck is achieved by a shaft which is connected to the vacuum chuck and powered by a motor.
In a typical photoresist coating process, a desirable amount of a liquid photoresist material is first applied to a top surface of the semiconductor substrate from a liquid dispenser that is mounted on a track while the substrate is rotated at a low speed on the vacuum chuck. The photoresist liquid spread radially outward from the center of the semiconductor substrate where it is applied towards the edge of the semiconductor substrate until the entire top surface of the substrate is covered with a thin layer. Excess photoresist liquid spun off the rotating wafer during the photoresist coating process. The rotational speed of the vacuum chuck and the amount of the photoresist liquid applied at the center of the semiconductor substrate can be determined and adjusted prior to and during an application process such that a predetermined, desirable thickness of the photoresist is obtained. The rotational speed of the vacuum chuck is normally increased at the end of the application process to ensure that the entire surface of the substrate is evenly coated with the photoresist material.
A conventional apparatus for coating photoresist on a semiconductor substrate is shown in FIG. 1. The apparatus 10 consists of a drain cup 12 and a rotating platform 20, i.e., a vacuum chuck, positioned at the center of the drain cup for supporting a semiconductor substrate 26 positioned on a top surface 24 of the vacuum chuck 20. The vacuum chuck can be rotated by a shaft 32 which is connected to an electric motor (not shown). The drain cup 12 is provided with a spent photoresist drain pipe 34. The spent photoresist drain pipe 34 is used to drain away photoresist liquid that spun off the substrate during a coating operation.
In the operation of the conventional coater 10 of FIG. 1, the vacuum chuck 20 is first loaded with a semiconductor substrate 26 on top. A liquid dispenser 18 then approaches the center of the substrate 26 and applies a predetermined amount of a liquid photoresist material to the center of the substrate. The vacuum chuck 20 then starts spinning to spread out the photoresist material to evenly cover the top surface 24 of the substrate 26. Extra photoresist material is thrown off the substrate surface and drained away by the drain pipe 34.
When a lithographic process is carried out on a photoresist layer, any foreign particles or defects in the pattern formed on the photoresist layer act as extra etch mask and are reproduced on the substrate surface. Certain types of these extra resist pattern have been identified as originating from the photoresist coating process, i.e., photoresist powder or gel that bounces back onto the substrate surface during the high speed spinning step of the coating process. The extra resist pattern on the substrate surface causes serious defects in the substrate and thus, greatly reduces the yield of the chip fabrication process.
In certain fabrication processes for IC devices, a series of photoresist coatings are applied on top of a wafer in order to fabricate the device. For instance, a series of photoresist coatings such as a bottom anti-reflective coating (BARC), a photoresist coating and a top antireflective coating (TARC) are frequently deposited on a semiconductor structure for defining a specific feature of the circuit. After the photolithographic process is completed, a solvent is used in an edge-rinse process for removing any residual coating material from the edge of the wafer. The photoresist material used in the BARC and TARC are frequently the same. However, they are different than the material used for the photoresist layer sandwiched in the middle. The solvent utilized is also a completely different chemical than that used in the photoresist layer.
In a conventional semiconductor fabrication process, at least two or three spin coating chambers must be used to coat the different photoresist materials in order to avoid the mixing of the different types of photoresist liquids resulting in chemical reaction and the generation of debris or particles in the reaction. The debris or particles generated present a serious contamination problem to the wafer. Furthermore, the mixing and the resulting chemical reaction between the different types of photoresist liquids and the solvent further clogs the drain pipe for the drain cup that surrounds the wafer. This leads to further contamination problems.
It is therefore an object of the present invention to provide liquid coating apparatus for processing different types of photoresist liquids without the drawbacks and shortcomings of the conventional liquid coating apparatus.
It is another object of the present invention to provide a liquid coating apparatus that is adapted for dispensing two different liquids without causing contamination problems.
It is a further object of the present invention to provide a liquid coating apparatus that is adapted for dispensing two different liquids without contamination problems by utilizing two separate drain cups.
It is another further object of the present invention to provide a liquid coating apparatus that utilizes two separate drain cups mounted concentrically with one on top of the other.
It is still another object of the present invention to provide a spin coating apparatus that utilizes an upper drain cup and a lower drain cup mounted concentrically wherein the upper drain cup is constructed in two halves adapted for outward movement to allow a wafer chuck to be lowered into the lower drain cup for performing a second coating step.
It is yet another object of the present invention to provide a spin coating apparatus adapted for dispensing two different liquids by utilizing an upper drain cup and a lower drain cup mounted concentrically wherein the upper drain cup may be moved out of the way by robot arms.
It is still another further object of the present invention to provide different liquids in the same spin coating apparatus by utilizing an upper drain cup and a lower drain cup mounted concentrically to perform a first coating step in the upper drain cup, followed by removing the upper drain cup outwardly such that a wafer chuck may be lowered into the lower drain cup for performing the second coating step.
It is yet another further object of the present invention to provide a spin coating apparatus for sequentially dispensing two different liquids on a wafer surface which includes an upper drain cup and a lower drain cup each adapted for handling a different liquid wherein the upper drain cup is operated by robot arms for outward movement of the two halves in order to operate the lower drain cup for the second coating process.